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Old March 20th, 2004, 09:30 PM   #586
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Filip: Thanks for that link! Stuff like that helps me out a lot.

If we could get a ground glass with grain fine enough to be acceptable for the high megapixel still cameras, it should be more than good enough for a DV camera.
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Old March 20th, 2004, 10:54 PM   #587
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if you want to test the size of the grain on your gg, just point a laser in one end of your adapter and shine the output against a white surface. This magnifies the grain so you can see it.
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Old March 20th, 2004, 11:27 PM   #588
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Frank,

This second round of grabs looks great!!! So much better than the first. You must be getting excited about your adapter. I have just a few quick questions to help me appreciate what you've posted even more.
What size and F# SLR lens are you using?

How much of the original SLR image on the GG are you shooting? Are you zoomed in at 36mmx24mm or are you wider? (I get rid of my hotspot & vignetting when I zoom in onto the GG image but I'm afraid I'm tighter than 36mm & 24mm and so am losing some benefit of 50mm SLR lens vs. shooting with vid cam's original long lens)

How bright was the day you were shooting in? Time of day?

The images had a definate blue hue to them. Do you think that was the polarized GG?

I also noticed some slight barell distortion with the image of the post and the planks. Do you think your condenser is too strong? I had the same distortion when using a wide angle SLR zoom lens(35mm at F3.5) with a thick condenser. The distortion went away with a 50mm 1:1.4 lens with the same condenser. I haven't had any luck with a WA lens yet. 45mm is the shortest I've been able to use without distortion or hotspotting and vignetting.

Thanks for sharing, Joe
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Old March 21st, 2004, 12:42 AM   #589
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John: Thanks for the tip! I'll have to find a laser now. :-) I notice when holding the camera at certain angles and a flare hits it, the grain is really easy to see.

Joe: Thanks!

The lens I'm using is a Pentax 1:2 50mm.

Having a lens on each side of the groung glass, I get an evenly bright image. (I can actually stop down the aperture on the 35mm lens and not get a hotspot. However, the grain starts to jump out at that point.) Honestly, I have been just zooming in until I don't see the outer ring of the adapter. Not too precise. I may be tighter than 36x24mm.

The time of day was around 1:00. Brighter than when I shot the other images.

About the blue hue: It could have been the polarizer, or I may not have had the white balance doing the right thing. Next time I will white balance off something.

The distortion is really noticeable when panning around. My condenser may be too thick. I'm trying to get some more lenses to play around with. Maybe I can verify if it is condenser thickness.

Thanks for checking the images out!

,Frank
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Old March 21st, 2004, 02:24 AM   #590
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Frank-
First of all nice work. To narrow down if your getting distortion from your 35mm lens or your condenser do this simple test:

Focus on something at infinity with a film lens 50mm or longer. Find something that has straight lines and put that line near the outer area of your frame. If that line looks curved then its your condenser lens that causing the problem.

What you'll need to do is find a different condenser that has the closest to a F1 rating or higher. Now when I say F1 I DO NOT mean f stops. Instead a condenser that has a F1 rating is one that has a focal length equal to its diameter. If you have a lens that has a focal length shorter than its diameter then you will begin to have spherical distortion like you discribed. On the other hand if you have a lens that has a longer focal length then its diameter you will not but as that focal length gets longer its ability to culminate light diminishes. From my experience it generally is best to go with a condenser with a focal length the same or slightly longer than its diameter.

Also make sure to get a condenser a least 5mm larger in diameter then what a 36mm X 24mm image will allow due to the optical quality of lenses at their very edges.

-Brett Erskine
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Old March 21st, 2004, 02:50 AM   #591
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Condenser

Brett thanks for your explination about condenser lens.

Why you hare talking about frame 24mmX36mm

i test whit 27mmX36mm 4:3 ratio and is working just fine

and watt abour chromatic aberations ????
some one find doublets (crow-flint) lens ????
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Old March 21st, 2004, 03:08 AM   #592
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just to check - you are talking of condenser in this position:

|)(|

yes?

filip
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Old March 21st, 2004, 08:21 AM   #593
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Condenser Lens clarification

Brett,

Thanks for clarifying the F1 condenser rating. I now better understand a message you posted a while back. So to clarify...
(1) 50mm dia. PCX with a FL=50mm is F1?
(2) 50mm dia. PCX with a FL=100 mm ea. is also F1?

Based on how my Minolta has the rectangular condenser set up in the focus plane, I'd guess the configuration for adapter as follows. Please correct me if this is wrong.

Single PCX....... SLR] l) [Vid Cam (flat surface of PCX is GG) ???

double PCX ....... SLR] (ll) [Vid Cam (flat surface of 2nd PCX is GG) ???

The above is a question not a statement of fact. Thanks for the help, Joe
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Old March 21st, 2004, 04:02 PM   #594
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1)Yes
2)No. Greater than F1

Yes
Yes
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Old March 21st, 2004, 06:00 PM   #595
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I got a little confused from the last couple posts. Brett, your explanation of F1 makes total sense. A 50mm focal length would be ideal for a 50mm diameter PCX lens. In an earlier post, you stated
Quote:
If you cant find the FL you want then use two PCX lenses (one on each side of the GG) with two times long focal length for each lens. They will work together to shorten the FL to where you want
So essentially, considering the lenses are all the same diameter, two 100mm focal length lenses in series are equal to one 50mm focal length lens. That is what Joe seemed to be asking earlier, but you stated that it wasn't correct. It looks like the (1) and (2) may have caused a little confusion, so I'd just like to double check.

One 50mm focal length PCX lens with 50mm diameter = F1.
Two 100mm focal length PCX lenses with 50mm diameters > F1?
Two 50mm focal length PCX lenses with 50mm diameters = ?
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Old March 21st, 2004, 08:36 PM   #596
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Brett: Thanks on the images, and thanks for that detailed explanation! That makes sense about having a larger condenser due to image quality at the edges. I will experiment further and try that test. I will try to post something when/if I make any progress.
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Old March 22nd, 2004, 10:41 PM   #597
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One 50mm focal length PCX lens with 50mm diameter = F1.
*Yes

Two 100mm focal length PCX lenses with 50mm diameters > F1?
*Yes, in the sense that the two lenses would work together to shorten the focal length to 50mm. As to whether you could give the TITLE of F1 to two lenses working in series Im not sure (probably not) but who care. I only mention it in case you guys are shopping for two lenses and hoping it will state their combined F number.

Two 50mm focal length PCX lenses with 50mm diameters = ?
*25mm. A interesting thing about this example is I believe (but Im not sure) that by combining two lenses with F1 ratings you get the best of both worlds. A shorter focal length and no spherical distortion.

Does that help?

-Brett Erskine
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Old March 23rd, 2004, 01:16 AM   #598
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Yeah, that helps a lot. If you have any more pointers, I'd love to hear them. Thanks for the help Brett.
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Old March 23rd, 2004, 09:33 PM   #599
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PCX lens questions

Where are you guys finding the best PCX lens?

Has anyone found PCX lens already mounted?
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Old March 26th, 2004, 06:33 PM   #600
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Hate to be the newbie, but what does PCX stand for, and in lamens terms, what make PCX such a good choice?
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